The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Can Mounjaro Affect Pregnancy?
If you're taking Mounjaro (tirzepatide) and planning to become pregnant, or are currently pregnant, you should stop the medication and speak with your GP immediately. Mounjaro is not recommended during pregnancy because there is not enough safety data in pregnant people. This guide covers what the evidence shows, what NHS guidance recommends, and what to do if you're thinking about starting a family while on this weight management injection.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
What the Evidence Shows About Mounjaro and Pregnancy
Mounjaro has not been adequately studied in pregnant people, which is why it is classified as unsuitable for use during pregnancy in the UK. The product information states that women should not become pregnant while taking tirzepatide, and if pregnancy is suspected, the medication should be stopped immediately and a GP consulted.
Animal studies have shown some effects on foetal development at high doses, but these findings don't always translate to humans. However, the lack of human pregnancy data means prescribers and healthcare professionals take a cautious approach. No medication is prescribed during pregnancy without clear evidence of safety, and Mounjaro falls into this category.
If you are taking Mounjaro and planning pregnancy, discuss this with your prescriber well in advance. They may recommend stopping the medication several weeks before attempting conception to allow it to clear from your system.
Clinically BackedWeight Loss
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Contraception and Mounjaro — What You Need to Know
If you are a woman of childbearing age taking Mounjaro, using reliable contraception is essential. The product information recommends that women using oral contraceptive pills add a barrier method (such as condoms) for 4 weeks after starting Mounjaro and 4 weeks after each dose increase. This is because Mounjaro may slow stomach emptying and reduce how quickly oral medications are absorbed, potentially reducing contraceptive effectiveness.
If you rely on oral contraception, discuss this with your GP or prescriber. They may suggest switching to a non-oral contraceptive method (such as an implant, injection, or coil) for the duration of your Mounjaro treatment, or using additional barrier protection throughout.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is it safe to take Mounjaro if I'm trying to get pregnant?
No. Mounjaro should not be used if you are trying to become pregnant or suspect you are pregnant. Stop the medication and contact your GP immediately if pregnancy is suspected. Discuss your family planning intentions with your prescriber in advance so they can support you appropriately.
How long should I wait after stopping Mounjaro before trying to conceive?
Mounjaro (tirzepatide) has a relatively short half-life of about 5 days, meaning most of it clears from your body within 2–3 weeks. However, your prescriber may recommend waiting longer for complete clearance. Discuss the timing with your GP or the prescriber who manages your Mounjaro treatment.
Does Mounjaro affect fertility in women?
There is limited evidence on Mounjaro's direct effects on fertility. However, modest weight loss can improve fertility in some women with obesity-related infertility. If you have concerns about fertility, discuss these with your GP before starting or continuing Mounjaro.
What contraception should I use with Mounjaro?
If taking oral contraceptive pills, add a barrier method (condoms) for 4 weeks after starting and after each dose increase. Consider switching to a non-oral method like an implant or coil for the duration of treatment. Your GP or prescriber can advise on the best option for you.
What should I do if I became pregnant while taking Mounjaro?
Stop taking Mounjaro immediately and contact your GP or midwife. Inform them that you were taking tirzepatide. They will assess whether any further monitoring is needed. Early pregnancy support and counselling should be offered by your NHS healthcare team.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.